Doyen is reportedly due to receive 75 percent of the defender's fee if he moves on and United are said to have offered 16 million pounds for the Argentina international.

But the Portuguese club, who do not want to sell Rojo, claimed Doyen CEO Nelio Lucas sent their president Bruno de Carvalho abusive text messages and launched an attack on the company for their behaviour and negotiating tactics.

Doyen had issued a statement warning Sporting that, while accepting they cannot force the Portuguese club to sell him, they were willing to pursue legal avenues to ensure they did not suffer.

But Sporting responded with a lengthy statement on their official website accusing Doyen of going against their wishes by trying to engineer a move for the left-back.

They said: "On July 23, Sporting's intention to keep the athlete was communicated, in light of which the player should have immediately been removed from the transfer market. Sporting was guaranteed that this would be the case and that the club's will would be respected.

"Surprisingly, it was only after that exchange that Sporting was confronted with offers for the player. As of that time and in going against that which was agreed, meetings were held between various clubs and Doyen to make offers for the player Marcos Rojo."

Sporting accused Doyen of masquerading as representatives of a club that wanted to buy Rojo in a meeting.

They said: "Sporting became aware that Doyen took part in the resulting meeting, namely by convincing the member of Sporting's board of directors that the person in question was a member of the visiting club and not in fact the CEO of Doyen. The situation was masked to such a degree that the person in question did not at any time speak in Portuguese, communicating at all times in the language used by the visiting club."

Sporting also allege that Doyen threatened that Rojo would become a disruptive influence at the club if he was not allowed to leave.

They stated: "In light of the seriousness of statements being made and falsities being communicated, we have been forced to reveal that at the beginning of the 13-14 season, that same CEO sent various abusive text messages to the president of Sporting, including one which stated in capital letters: 'MARCOS ROJO IS GOING TO [THE FOREIGN CLUB]' and that 'IF YOU DO NOT LET HIM HE WILL BEGIN TO CAUSE PROBLEMS IN THE ACADEMY.'

"While being further clear evidence of the interference that Doyen generates with those who it calls its partners, it became obvious that this is a reoccurring tactic, with only the name of the club being altered."

Rojo has been disciplined by Sporting for reportedly refusing to train in a bid to engineer his exit while it has been claimed that Doyen is entitled to a payment worth three-quarters of an offer they reject for the defender -- which in this case would earn it 12 million pounds.

Doyen's statement read: "Sporting is entirely within its rights not to transfer the player Marcos Rojo, knowing that it only has to make up for the fund under the terms and deadlines as contractually established since the beginning."

It added they "will not hesitate to use all legal resources at our disposal to defend fully all our interests and rights."